In this article, theoretical models and experimental data coalesce to elucidate structural aspects of glasses produced using sol-gel and melting methods in the SiO2CaOMgONa2OP2O5 system. The influence of the network connectivity on the in vitro bioactive behavior is disclosed. To achieve an accurate prediction of the bioactive response, an empirical method to determine the effective composition of the sol-gel glasses is first proposed. Finally, the bioactivity limits of glasses as a function of their effective composition was established.